1. Field of the Invention
The present invention relates to the field of power distribution, sequencing and controlling and, more particularly, to alternating current (AC) power distributors, sequencers and controllers.
2. Description of the Related Art
FIG. 1 shows a prior art AC power sequencer/controller 20 coupled to a load 23 which is, in this example, a computer system. AC power sequencer/controller 20 has multiple electrical outlets such as Ma 24, Sa 25, Sb 26, Sc 27 and Sd 28 that are connected to various electrical devices (e.g., a computer host 10, a printer 12, a modem 13, a display monitor 14 and an external storage device 15). AC power sequencer/controller 20 controls providing power from an AC power unit 22 to the electrical outlets 24, 25, 26, 27 and 28 so that the electrical devices 10, 12, 13, 14 and 15 can be turned on/off in sequence. AC power unit 22 can be an AC outlet or other AC power source.
In the computer system shown in FIG. 1, it may be desirable to provide power to or disconnect power from the master unit (Ma 24) first and then the slave units (Sa 25, Sb 26, Sc 27 and Sd 28). To perform this task, prior art AC power sequencer/controller 20 includes a feedback cable 21 coupled between computer host 10 and Ma 24 to ensure that peripherals 11 including printer 12, modem 13, display monitor 14 and external storage device 15 are turned on/off after computer host 10 is turned on/off. The sequence of an operation may include the following: after AC power sequencer/controller 20 provides power to computer host 10, AC power sequencer/controller 20 waits for a feedback signal from computer host 10 through feedback cable 21 notifying AC power sequencer/controller 20 that computer host 10 is turned on. Upon receiving the feedback signal, AC power sequencer/controller 20 provides power to peripherals 11. A similar procedure can be adopted for removing power from the computer system.
While AC power sequencer/controller 20 is used to turn on/off computer host 10 and peripherals 11 in sequence, it can also be used to minimize power surges in a server system. The prior art AC power sequencer/controller 20 having feedback cable 21 may be utilized in a server (or a rack) system which may include many switching power supplies. Without an AC power sequencer/controller, a huge in-rush current can flow when AC power is applied to the server system. It is easy to trip a circuit breaker either in the server system or on a user's AC power supply panel if all the power supplies are turned on at the same time. A feedback cable is provided in such a server system to turn on various system components at different times instead of turning them on all at once to reduce the amount of power surge.
The drawbacks of these prior art solutions include the cost and low reliability of the feedback cable(s).
The present invention provides a method and apparatus for controlling and sequencing AC power distribution by sensing the current through various electrical outlets rather than using one or more feedback cables.